Instrumentation for the production of fixing surfaces for a knee joint endoprosthesis

ABSTRACT

In an instrumentation for the production of fixing surfaces for fixing a knee joint endoprosthesis to the femoral condyle that is adjacent to the knee, and to the tibial head, provision is made for a rotary milling head, which is fixable in relation to the longitudinal axis of the femur and tibia, respectively, by fastening means and which, in relation to this longitudinal axis, is angularly adjustable in a stable stop position by being pivoted, defining milling planes, and which is displaceable in the set milling plane, covering same and working as a face milling cutter or as a cylindrical milling cutter.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to an instrumentation for the production offixing surf aces for a bee joint endoprosthesis on the femoral condylethat is adjacent to the knee joint and on tie tibial head.

[0003] 2. Background Art

[0004] A knee joint prosthesis of the type under regard is described forinstance in DE 41 02 509 C2, FIG. 3 of which illustrates in particularthe fixng surfaces needed for implantation of the part of the prosthesison the femoral side, i.e, for fixing to the end of the thigh on the sideof the knee. This plurality of fixing surfaces which are disposed at anangle to each other is conventionally produced by a rod, which extendsin the axial direction of the bone, being inserted in the medullaryspace after exposure of the bones; by the aid of a saw template which isfixed to the rod and directly to the bone, the individual planes aresawed successively by means of a saw.

[0005] Positioning the templates non-displaceably during sawing requiresextensive implementation, however really perfect and nondisplaceablepositioning will not be attained successfully. Moreover, the necessaryprocesses are complicated, leading to comparatively high inaccuracy andunnecessarily long operation times, which places strain on the patientand ultimately also on the operating surgeon. The conventionalpreparation of these fixing surfaces is specified in detail for examplein the leaflet entitled “MC-KNIEGELENK nach Prof. Dr. Diehl”, page 5 f.

SUMMARY OF THE INVENTION

[0006] It is an object of the invention to embody an instrumentationwhich will ensure a simple, rapid and accurate way of preparing thefixing surfaces needed for implantation of he tibial part and inparticular the femoral part of a prosthesis.

[0007] According to the invention, this object is attained by a rotarymilling head which is fixable in relation to the longitudinal axis ofthe femur and tibia, respectively, by fastening means and which, inrelation to this longitudinal axis, is angularly adjustable in a stablestop position by being pivoted, defining milling planes, and which isdisplaceable in the set milling plane, covering same and working as aface milling cutter or as a cylindrical milling cutter.

[0008] As a result of the design according to the invention, thefundamental problems of conventional sawing by the aid of a template nolonger occur. Moreover, after treatment and fine machining (subsequentadjustment) are possible, should this be necessary or desirable.

[0009] By advantage, the fastening means comprise clamps which enclaspthe respective bone.

[0010] In this case, a first clamp may grip the bone from above, theclamp having two jaws which are displaceable one in relation to theother and fixable in a stop position.

[0011] The fastening means may comprise at least a second clamp, thelegs of which are approximately parallel to the longitudinal axis of thebone and displaceable one in relation to the other, with fasteningthorns and/or holes into which to insert fastening screws being formedon the ends of the legs.

[0012] The thorns provided according to the invention ensure preliminaryadjustment for holes to be drilled in the bone for the fastening screwsor during the screwing process. The milling equipment can be detachedfrom the fixing component at any time and later on it can be fastenedagain precisely in its initial position by quick-acting closures.

[0013] Preferably the milling head is designed for adjustment in heightso that corresponding setting is possible for a certain fixing surfaceto be formed. Height adjustment may advantageously be put into practiceby a threaded spindle of a stable or stabilizable stop position.

[0014] In keeping with a preferred embodiment it is provided that, withthe milling angle set, the milling head is linearly translationallydisplaceable via guide bars and movable via a pivot bearing or crosssupport so that a milling plane is defined in this way which can beworked successively by the milling head. The milling head has acylindrical configuration with the surface of the cylinder forming themilling surface and the front of the cylinder running preferablyparallel to the milling plane.

[0015] By advantage, further provision is made for an equipment forpresetting the position of the axis of the leg, it being possible in hisway to consider whether the patient has a varus-valgus deformity. Alsoleg rotation (varus or valgus deformity) can be corrected and adjustedaccurately.

[0016] Furthermore, provision is made for equipments setting the lengthof a leg and the size of the prosthesis.

[0017] In the scope of the invention, it is possible to move the millinghead or milling cutter manually, using the guide according to theinvention.

[0018] By alternative, actuation in particular by servo motor can beprovided for, the setting equipments and/or the motion of the millinghead in the milling plane, triggering of the servo motors beingadvantageously computer controlled. Correspondingly, it is possible tomake the whole operation computer-controlled, in particular also independence on X-ray or computer tomography images.

[0019] For navigation purposes and in replacement of manual handling andsetting of the milling head, the instrumentation may be equipped withinfrared markers in order for computer controlled setting to bepossible, combined with a three dimensional computer animation on thedisplay screen which has been obtained by a preceding computertomography.

[0020] Details of the invention will become apparent from the ensuingdescription of a preferred embodiment taken in conjunction with thedrawing.

BRIEF DESCRIPTION OF THE DRAWING

[0021]FIG. 1 is a plan view of the instrumentation according to theinvention with the milling cutter being positioned horizontally;

[0022]FIG. 2 is an illustration, corresponding to FIG. 1, with themilling cutter being positioned vertically;

[0023]FIG. 3 is a side view with the milling cutter being positionedperpendicularly in the cutting plane I;,

[0024]FIG. 4 is a side view, corresponding to FIG. 3, with the millingcutter being positioned perpendicularly in the cutting plane II;

[0025]FIG. 5 is a corresponding side view with the milling cutter beingpositioned perpendicularly in the cutting plane III;

[0026]FIG. 6 is a corresponding side view with the milling cutter beingpositioned in parallel to the cutting plane IV;

[0027]FIG. 7 is a side view with the milling cutter being positioned inparallel to the cutting plane V;

[0028]FIG. 8 is a front view with the milling cutter being positionedvertically; and

[0029]FIG. 9a to 9 f are illustrations of a femoral bone and theposition of the milling cutter relative to the femoral bone as well asthe cutting planes I to V produced on the femoral bone by means of themilling cutter.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0030] The drawing illustrates a milling cutter 1 with a milling head 2which is driven in rotation and may function as a cylindrical millingcutter with its surface area 3 being used as well as a face millingcutter with its frontal surface 4 being used. When the cutting planes Ito III are prepared—as described below—the milling head 2 is employed asa face milling cutter, whereas it is employed as a cylindrical cutterfor the preparation of the cutting planes IV and V.

[0031] The milling cutter 1 is lengthwise displaceable in the directionof the double-headed arrow 8 of FIG. 1 on an x-guide 5 which comprisestwo parallel bars 6, 7.

[0032] By means of a mounting 9, the x-guide 5 is fastened on a bearingblock 10, from which a y-guide 11 extends in a direction vertical of thex-guide 5; the y-guide 11 also comprises two bars 12, 13, enabling themilling cutter 1 to be displaced for up and down adjustment in thedirection of the double-headed arrow 14 in FIG. 2.

[0033] The bearing block 10 is further equipped with a disk cam 15 whichensures various pivoting angles to be set in stable stop positionscorresponding to the cutting planes I to V; the stop positions arefixable by a locking screw 16.

[0034] A setting block 18 is joined to the bearing block 10 via an arm17, this setting block 18 ensuring a pivoting motion about a pivot axis19 which is positioned outside the setting block 18; a scale 20cooperates with a stationary marking 21 for corrective setting in thecase of lateral concavity or convexity of the leg (vanis-valguscorrection), The advantage of this corrective arrangement resides inthat any setting or adjustment will not affect the other axes.

[0035]FIG. 3 illustrates recesses 22 in the disk cam 15 which serve forsetting the milling planes I to V. FIG. 3 further shows a detent 23enabling the milling cutter 1 to be used as a face milling cutter, themilling cutter 1 is pivotal along the curvature 24 by 90°, arresting inthe detent 25 where it works as a cylindrical milling cutter.

[0036]FIG. 3 further illustrates a bone clamp 26 which comprises threejoined-on clamp pieces 27, 28, 29 each with a thorn 30 standing out;this bone clamp 26 is easily detachable by way of a quick acting closure30 a.

[0037]FIG. 3 further clearly shows a setscrew 31 for anterior-posteriorsetting as well as a dovetail guide 32 for medial-lateral setting.

[0038]FIG. 4 is a view corresponding to FIG. 3 in which the millingcutter 1 is positioned perpendicularly on the cutting plane II,preparing same by way of face milling.

[0039] In the position seen as a side view in FIG. 5, preparing thecutting plane III takes place by way of face milling, i.e. the millingcutter 1 is positioned perpendicularly in the cutting plane III.

[0040] The arrow 33 illustrates that the milling cutter 1 which works asa femoral cutter can be employed as a tibial cutter by being pivoted inthe direction of the arrow 33.

[0041] Proceeding from the position seen in FIG. 5, pivoting the millingcutter 1 or the milling head 2 takes place along the curvature 24 in thedirection of the arrow 34 into the position seen in FIG. 6 where themilling cutter 1 is used as a cylindrical milling cutter with itssurface area 3 being employed for the preparation of the cutting plane Vby the milling cutter 1 running parallel to this cutting plane V

[0042] When set as seen in FIG. 7, the milling cutter 1 equally works asa cylindrical milling cutter by being displaced parallel to the cuttingplane, producing same.

[0043]FIG. 8 is an elevation with the milling cutter 1 positionedvertically. Again the bone clamp 26 is visible, the central joined-onclamp piece 28 being adjustable by way of a guide 35 in the direction ofthe double-headed arrow 36 for the bone to be fixed or released.

[0044]FIG. 8 illustrates a setscrew 37 which acts on a self-locking wormgear for setting the inclination in cooperation with a stationarymarking 38 and a pivotal scale 39.

[0045] The following is another explication of the mode of operation ofthe instrumentation according to the invention, taken in conjunctionwith FIG. 9:

[0046] As seen in FIG. 9a, the first cutting plane 1 is prepared by wayof face milling, the frontal face 4 of the milling head 2 beingpositioned vertically in the cutting plane 1. In this case, theinstrumentation has the setting seen in FIG. 2.

[0047] Then the cutting plane II is produced also by way of facemilling, which is illustrated in FIG. 9b, with the instrumentationhaving the setting seen in FIG. 4.

[0048] Subsequently, the cutting plane III is produced by face milling,the instrumentation having the setting of FIG 1.

[0049] This is followed by a conversion from face milling to cylindricalmilling as illustrated in FIG. 6 as compared to FIG. 5. Now the surfacearea 3 of the milling head 2 is used for milling and moved along thecutting plane IV, i.e. parallel thereto, as seen in FIG. 9d. This isfollowed by the preparation of the cutting plane V by cylindricalmilling, which is seen in FIG. 9e.

[0050]FIG. 9f is a combined illustration of how the individual cuttingsurfaces I to V are successively produced.

What is claimed is
 1. An instrumentation for the production of fixingsurfaces for a knee joint endoprosthesis to be fixed to the femoralcondyle that is adjacent to the knee, and to the tibial head,characterized by a rotary milling head (2) which is fixable in relationto the longitudinal axis of the femur (40) and tibia, respectively, byfastening means and which, in relation to this longitudinal axis, isangularly adjustable in a stable stop position by being pivoted,defining milling planes (cutting planes I to V), and which isdisplaceable in the set milling plane (cutting planes I to V), coveringsame and working as a face milling cutter or as a cylindrical millingcutter.
 2. An instrumentation according to claim 1 , characterized inthat the fixing means comprise joined-on clamp pieces (27, 28, 29) whichenclasp the respective femur (40).
 3. An instrumentation according toclaim 1 , characterized in that a first clamp grips over the femur (40)from above, with the clamp (26) having joined-on clamp pieces (27, 28,29) which are displaceable one relative to the other and fixable in astop position.
 4. An instrumentation according to claim 1 ,characterized in that at least one of fastening thorns (30) and holesinto which to insert fastening screws are formed on the ends of thejoined-on clamp pieces (27, 28, 29).
 5. An instrumentation according toclaim 1 , characterized in that the milling head (2) is adjustable inheight.
 6. An instrumentation according to claim 1 , characterized inthat a setscrew (31) for a threaded spindle of a stable stop position isprovided for height adjustment.
 7. An instrumentation according to claim1 , characterized in that the milling head (2) is linearlytranslationally displaceable in the milling planes via guide bars (5,11) and pivotal by a pivot axis (16) or cross support.
 8. Aninstrumentation according to claim 1 , characterized in that apre-setting equipment (17, 18) is provided for setting the position ofthe axis of the leg.
 9. An instrumentation according to claim 1 ,characterized in that a setting equipment for the length of a leg(setscrew 31) is provided.
 10. An instrumentation according to claim 1 ,characterized in that a setting equipment for the size of the prosthesisis provided.
 11. An instrumentation according to claim 1 , characterizedin that at least one of the setting equipments and the motions of themilling head (2) in the milling planes (I to V) are servo motor driven.12. An instrumentation according to claim 1 , characterized in thattriggering the servo motors is computer-controlled.
 13. Aninstrumentation according to claim 1 , characterized in that infraredmarkers are provided for navigation.